JPS58170505A - Separation of glycol from electrolyte containing aqueous solution - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separating glycol from an electrolyte-containing aqueous solution.

Glycols are defined here as alcohols and alkoxyalcohols with two OH groups, thus they are e.g. ethylene glycol C/, 2-ethanool), propylene glycol C/, 2'-fr:
I pandiol), trimethylene glycol (7,3-
7'ropanol], diethylene glycol (HOC
2H40C2H40H) and triethylene glycol (HOC2H40C2H40C2H40H).

Glycols are moderately soluble in water, and glycols with more or less than 7 carbon atoms are even readily soluble in water.

The present invention particularly relates to a method for the separation of glycol from an electrolyte-containing aqueous solution by separating a fraction with an increased glycol:electrolyte ratio from the electrolyte-containing aqueous solution by means of a semipermeable membrane and then recovering the glycol from the fraction. . Such methods are known and are obtained from salt-containing wastewater from an ethylene oxide production plant by direct oxidation, by subjecting the wastewater filled with salt and glycol to reverse osmosis through a semi-permeable membrane using pressure. According to ethylene glycol, approximately 6θ% of the glycol present in the water can be recovered in one shot; the rest has to be discharged as countercurrent along with the salt-making solution, or is further processed at high cost. must be processed.

It has now surprisingly been found that when a solution containing both glycol and electrolyte is subjected to electrodialysis, a stronger separation of glycol from the electrolyte-containing aqueous solution can be achieved.

The present invention therefore provides a method for separating glycol from an electrolyte-containing aqueous solution by separating a fraction with an increased glycol-ni-electrolyte ratio from the electrolyte-containing aqueous solution by means of a semipermeable membrane, and then recovering the glycol from said fraction. , a method characterized in that electrodialysis is used for the separation of the fractions.

Electrodialysis is originally a well-known technique for the deionization of aqueous solutions, especially for the production of drinking water, but surprisingly, glycols can be used to remove salts very effectively without any negative impact on the process. can be removed from the glycol and water mixture. Even a glycol content of 1 or more in the aqueous solution is acceptable. According to the invention, at least goq6 of the amount of glycol initially present
can be separated and recovered, and often even more than tS.

Electrodialysis is essentially a method that utilizes the selective movement of ions across a membrane due to an applied electrical potential difference. Some membranes pass almost exclusively cations (cation-selective membranes), and other membranes almost exclusively pass anions (anion-selective membranes), so that the acid solution Ion concentration can be increased or decreased. When an array of alternating anion-selective and cation-selective membranes is placed in a DC voltage electric field, the solution surrounded by the pair of membranes is diluted (diluent).
, and the solution surrounded by adjacent pairs of membranes becomes more concentrated (concentrated solution).

Any material that is practical for carrying out electrodialysis is suitable as a membrane material. Useful overviews of such materials and of the practical aspects of electrodialysis devices are found, for example, in R, E, L
acey and S. Loeb, eds.
alProcessing with Membrane
es”, Wi 1ey-Intersctence
+New York, / '? It is stated in 1972, page Otsu-7. However, instead of more or less common membrane materials, so-called tight-pore
It has been found that exceptionally good results are achieved when using a "membrane".

A more or less typical membrane will allow more water molecules to move through the membrane per amount of charge passed through than a tight pore membrane. This simultaneous movement of water is called electroosmotic flux.

The lower this flux, the higher the concentration the concentrate will have.

In current practice, anion-selective membranes with electroosmotic fluxes of about //j to 200 grams (water)/faraday (charge transferred) (lilF) are called general membranes, and about
/, t An anion-selective membrane with an electroosmotic flux smaller than f/IF is called a tight-pore membrane. Yang □＼
For ion-selective membranes these values are slightly higher: approx.
Those with an electroosmotic flux of 210 to 3009/F are called general membranes, and therefore those with values lower than about 2/01/F are called tight pore membranes. single tighthore
The total electroosmotic flux of a cell pair - one tight pore cation selective membrane and one tight pore cation selective membrane - is typically less than 300 g/F. Therefore, it is preferable to use electrodialysis cell pairs whose total electroosmotic flux is less than 30011/F.

Tight pore membranes have the additional and unexpected advantage that both glycol and water pass through more easily; in other words, the glycol concentration is lower in the electroosmotic flux than in the feedstock. It has been found that in a typical membrane, the ratio of glycol to water that migrates through the membrane is the same as the ratio they were present in the feedstock. The effectiveness of glycol separation is thus enhanced by the use of tight pore membranes.

Usually, the direct voltage applied between the anode and the cathode is advantageously up to t/l, tV, and preferably in the range of /J to no, tv, especially about 2V. Depending on the electrolyte concentration and type of ion, and thus the current density, this voltage may be set slightly higher or lower according to well-known techniques.

The process of the invention is particularly suitable for use in ethylene oxide plants.

In the production of ethylene oxide by direct acid process,
Carbon dioxide and water are formed in the side reaction C2H4+30 →2CO+2H20 2 and to a lesser extent also organic acids such as formic acid, which are neutralized with base and discharged with the water. At the same time carbonates, often alkali metals (
Bi9 carbonate is formed. The salt solution thus obtained also contains ethylene glycol and diethylene glycol resulting from the hydrolysis of ethylene oxide dissolved in the water. Ethylene oxide, which is otherwise present in the salt solution, is easy to remove by distillation, but the glycol remains with the salt in the water leaving the plant as a waste stream, which has a relatively low organic content but is Nevertheless, they are held highly responsible.

The total concentration of glycols and salts present in this wastewater is /
It varies within the range of j & Ig%W. Organic charges, on the other hand, lead to high treatment costs in biological clarifiers;
On the other hand, this results in a loss of glycol amounting to about 0.5% of the production of ethylene oxide. It is therefore desirable to recover the glycols present in this wastewater, and this has now been made surprisingly simple according to the invention. The invention therefore also includes a process for the production of ethylene oxide by direct oxidation, using the proposed process to separate the glycols produced in saline municipal wastewater by the hydrolysis of ethylene oxide.

Other applications are found in the dehydration of natural gas by using glycols, for example immediately after extraction or during pipeline transportation. When gas is produced in the reservoir, water and therefore some dissolved salts - mainly NaCl - are also entrained. The gas is then dried by absorption in a glycol, preferably triethylene glycol. In subsequent regeneration of this glycol, for example in a vacuum regenerator,
Salt deposits cause problems. These problems can be overcome by treating the glycol-water mixture according to the method of the invention, thus separating the small bleed of the salt making solution from the large flow of glycol and water. The bulk flow can then be fed to a vacuum regenerator.

The invention therefore also includes a process for drying brine-containing natural gas by using a glycol-rich method, wherein the glycol is regenerated after absorption of brine and subsequently separated by using the method according to the invention.

As a third application of the invention, the oligomerization of ethenoyl C1o- using a catalyst dissolved in butanediol
A method is proposed for the production of C2o alpha olefins, characterized in that the salt-contaminated butanediol is treated using the method according to the invention and recycled. For a more detailed description of this olefin production method, see E.
Che by R, Freitas and C, R, Gum
mical Engineering Progress
s (1979/Mon.), pages 73-7 Otsu.

The method according to the invention could also be used, for example, in the regeneration of glycol-water antifreeze mixtures for automobile engines.

The invention will be further illustrated by the following examples.

EXAMPLES Several experiments were carried out with glycol-water mixtures from an ethylene oxide plant. The salt consists of 0% HCOONa (sodium formate) and 70% Na2CO3 (sodium carbonate), while the majority of the glycol consists of ethylene glycol, and the remainder consists of oligocondensates, mainly noethylene glycol, the amount of which is depends on the glycol:water ratio. Since the various glycols show negligible differences in their membrane permeability (electroosmotic flux), the term "baglycol" will be used hereinafter as a collective concept and the exact composition will not be stated.

The electrodialysis device used was “Ionics Corpor
The so-called °° stack tsuku (5 tac
k Pack) "The laboratory apparatus is of a hydrodynamic design such that the results obtained therein can be immediately transferred to those of larger apparatuses. All experiments were carried out at 23°C. The effective membrane area was 0./7 m when both the conventional membrane and the tight pore membrane were used.The glycol content of the solution was measured by gas chromatography, and the Na content was determined by atomic absorption spectroscopy. It was measured by

Example/Glycol content of lAg and 33; 20 pp
A sample of 1 kg of solution with a Na content of mw is introduced as a stream to be desalinated into one inlet of the electrodialysis machine (diluent), while 37 g of deionized water with a Na content of 37 g is introduced as a stream to be desalted. kg was introduced into the other inlet (concentrate - person). 3. Dilution and concentration of salts and glycols in the electrodialyzer. caused by the effect of voltage on the OV/cell pair (diluent-out and concentrate-out).

In the electrodialysis, common membranes, i.e., anion-selective membranes (Ionics
Inc, code number 703 PZL3g O) and 2 p O,! A cation selective membrane (Ionics Inc, code number Otsu/AZL M Otsu) with an electroosmotic water transfer of 9/F was used. Further data and results are shown in Table 1.

Contains less water and more glycol than usual.
Samples from other streams from an ethylene oxide plant were treated in a similar manner to Example/. The data and results are shown in Table 1.

Example 3 The general membrane is a tight pore membrane, code number 20'l
-UZL 3♂B (anion selectivity, electroosmotic flux)
VF) and code number Otsu/CZL3g Otsu (cation wettability, electroosmotic flux/gOg/F). Further experimental data and results are shown in Table 1.

1 tithe 4Φ3 seconds 11 111y's /ζme I! 2! Table 1 lists the numbers of known glycol conversion methods using the milliliter translucent method.

As learned from Jirl, the use of electrodialysis and reverse osmosis also removes a significant percentage of salts, but only the use of electrodialysis It makes it possible to recover more glycol, for example, 97 ＼ if you use qibo analysis, and 63 ＼ if you use reverse osmosis in 1 month.

It is now clear that tight pore membranes combine glycol retention and salt removal to give the best results.

Agent's name: Kawahara 1) - Ho 17-

Claims (1)

[Claims] (]) Glycol from an electrolyte-containing aqueous solution by separating a fraction with an increased glycol:electrolyte ratio from the electrolyte-containing aqueous solution by a semipermeable membrane, and then recovering the glycol from the fraction. A method for separating said fractions, characterized in that electrodialysis is used to separate said fractions. (2) The method according to claim 1, characterized in that a pair of electrodialysis cells whose total electroosmotic flux is smaller than 3001//F is used. (3) A method according to claim 1 or 2, characterized in that the applied DC voltage is in the range of 0 to lAtv. (4) Direct oxidation of ethylene oxide with N How to characterize it. (5) A method for drying natural gas containing salt water by using glycol, in which the glycol is regenerated after the salt water is concentrated, and in the regeneration step, the method according to claims 1 to 3 is used. A method characterized in that glycols are separated using a method. (6) C-C alpha 10 by oligomerization of edene using a catalyst dissolved in glycol
20. A method for producing refine, characterized in that glycol contaminated with salt is treated using the method according to claims 1 to 3 and recycled. (7) The method according to claim 1, wherein the glycol is butanediol.